refactor(runtime,packages,examples): named constants, package enums, idiom sweep

- runtime: HEADLESS_FRAME_PATH, STICK_DEADZONE / STICK_LEFT_X/Y, key and
  byte codes as char literals throughout (`k == 'w'`, `fill(rt_map, ' ', …)`)
- ludic.gameplay/stats: drop the duplicate `stat_field` (it answered "atk"
  for every build stat); Stats.base uses stats_field_name
- ludic.shooter: compare aim modes and fire patterns with AimMode.* and
  WeaponPattern.* instead of raw ints; STICK_RIGHT_X/Y
- ludic.npcai: DecisionMade / brain_set_state use AiState.*
- examples/games/menu.ludic uses Font.load / Ui.* with FONT_PATH and
  BACKDROP named; strings.ludic header says what it prints
- whole tree: `x = x + 1` → `x += 1` (single-term right-hand sides only),
  `0 - x` → `-x`, ASCII codes → char literals; every .ludic and every
  ```ludic fence reformatted with the fixed formatter (whitespace only)

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

examples/library/atlas.ludic

@@ -25,7 +25,7 @@ program AtlasDemo {
     let d = Sprite.define("hero", sheet, 2, 3)       # name a cell
     print(bi(Sprite.named("hero") == d))             # 1 — looked up by name
     print(bi(Assets.get("hero") == d))               # 1 — Assets.get is the same lookup
-    print(bi(Sprite.named("nope") == (0 - 1)))       # 1 — an unknown name is -1
+    print(bi(Sprite.named("nope") == (-1)))       # 1 — an unknown name is -1
 
     let whole = Assets.image("assets/kenney/tiny-dungeon/Tiles/tile_0096.png")
     print(Sprite.width(whole))                       # 16 — a whole tile as one sprite
@@ -34,7 +34,7 @@ program AtlasDemo {
     Screen.clear(0)
     Sprite.draw(whole, 10, 10)
     var n = 0
-    for yy in 10 .. 26 { for xx in 10 .. 26 { if Screen.pixel(xx, yy) != 0 { n = n + 1 } } }
+    for yy in 10 .. 26 { for xx in 10 .. 26 { if Screen.pixel(xx, yy) != 0 { n += 1 } } }
     print(bi(n > 0))                                 # 1 — the sprite drew content
   }
 }